Several types of memory modes are used on conventional motherboards, depending on how many dual inline memory modules (DIMMs) are installed. A single-channel (asymmetric) mode provides single-channel bandwidth operations when only one DIMM is installed or when the memory capacities of more than one DIMM are unequal. A dual-channel (interleaved) mode offers higher memory throughput and is enabled when the memory capacities of both channels are equal. A triple-channel mode provides triple-channel interleaving, which can reduce overall memory latency by accessing the DIMM memory sequentially. A quad-channel mode can be enabled when four (or multiples of four) DIMMs with identical capacity and speed are installed. Regardless of the memory mode used, each DIMM can operate only on a single channel.
Communication between the DIMMs and the motherboard can be done using differential uni-directional signaling or single-ended bidirectional signaling. When differential uni-directional signaling is used, more pins are needed to meet capacity demands for a given memory technology node, resulting in higher cost. Scaling capacity in point-to-point configurations has a direct impact on bandwidth. This is a disadvantage with respect to fly-by topologies where the bandwidth is constant for one DIMM or Many DIMMs. However, existing technology (channels, I/O's, etc.) are capable of running double data rate (DDR) data (DQ) signals at significantly higher data rates in point-to-point topologies.
It would be desirable to implement a flexible point-to-point memory topology.